feat(skills): add receipt evidence bundle

[zdfgu113]

Summary

• add a public receipt-evidence-bundle skill that turns caller-verified runx receipts into a reviewer-safe packet
• separate verified facts, bounded lineage inferences, missing evidence, reviewer actions, redactions, and public artifact links
• refuse malformed references and invalid verification verdicts
• include replayable evidence, a signed dogfood receipt, and a reviewer report

Verification

• runx-cli 0.6.13
• runx harness ./skills/receipt-evidence-bundle --receipt-dir /home/zjs/runx-frantic-receipts --json (3/3 passed)
• runx verify <dogfood-receipt> --receipt-dir /home/zjs/runx-frantic-receipts --json (valid: true, no findings)
• direct runner smoke test confirms sensitive-key redaction and no secret leakage

Frantic bounty #28.